Memory Management - Demystifying /3GB

re: Memory Management - Demystifying /3GB

bitzie — Mon, 26 Mar 2007 22:52:08 GMT

...but not on a SBS box.

Please do not use the /3 switch there.

I'll never have to explain /3GB again...

Clive Watson's Weblog — Tue, 27 Mar 2007 14:53:32 GMT

...I Hope! Well done to the performance team for their recent Windows Server articles, in particular

Performance team blog

Active Directory, Cluster and other fun stuff... — Wed, 28 Mar 2007 15:13:20 GMT

I see a lot of customers unnecessarily using the boot.ini /3GB switch. Explaining when and when not to

re: Memory Management - Demystifying /3GB

Jeff Louque — Fri, 30 Mar 2007 18:19:42 GMT

Keep in mind that the /Userva switch was introduced in Windows 2003 and does not work with Windows 2000.

re: Memory Management - Demystifying /3GB

Brad Rutkowski — Sat, 31 Mar 2007 00:05:29 GMT

You should aslo mention that 3GB and PAE dont like to play nice and should not be enabled together.

re: Memory Management - Demystifying /3GB

Jason Boche — Tue, 03 Apr 2007 21:38:28 GMT

"You should aslo mention that 3GB and PAE dont like to play nice and should not be enabled together."

That has not been my experience, but we only used the /PAE and /3GB tuning switch on one particular set of SQL cluster servers.

re: Memory Management - Demystifying /3GB

bday — Tue, 03 Apr 2007 22:32:20 GMT

"Brad Rutkowski said:

You should aslo mention that 3GB and PAE dont like to play nice and should not be enabled together."

This is incorrect. Our Exchange 2003 servers use the following and are quite happy.

/PAE /3GB /USERVA=3030* /BASEVIDEO

*2970 in some cases after some PTE tuning

Without /PAE we never see over 3.75GB of physical memory installed on this hardware set, so it helps out a lot.

re: Memory Management - Demystifying /3GB

Confused — Tue, 03 Apr 2007 23:17:23 GMT

>/3GB won't enable you to see the additional 4GB or 8GB of RAM you added to your new server

>/3GB doesn't necessarily make your application 50% more efficient

>/3GB should not be a standard for your environment (there are exceptions, and we'll get to those)

From the writing, I can't immediately tell: are these the myths? Or are these the "dispellations" ?

re: Memory Management - Demystifying /3GB

CC Hameed — Wed, 04 Apr 2007 00:06:42 GMT

The two sentences preceding the ones you cited should provide the context:

"At least once a week we have this discussion with a Systems Administrator somewhere who has this set in the boot.ini file on all of the servers but doesn't know why. Maybe someone added it to the server build process at some point or perhaps someone read about the /3GB switch somewhere and thought that it would improve performance or enable them to see the full 4GB or 8GB of physical memory installed on the system"

So, if you think of the bullet points as factual statements:

- /3GB should not be a standard for your environment (except in certain circumstances)

- /3GB won't enable you to see the additional 4GB or 8GB of RAM

- /3GB does not necessarily make your application 50% more efficient

Hope this clears up the misunderstanding!

Thanks for the feedback

Ask the Performance Team Blog

Carpe Diem: Flaphead.com @ Home — Mon, 09 Apr 2007 20:59:17 GMT

No sure how I found this blog but its damm good. Check out these that I have been reading today! IE7

re: Memory Management - Demystifying /3GB

Billy Dhillon — Wed, 11 Apr 2007 17:37:08 GMT

""Brad Rutkowski said:

You should aslo mention that 3GB and PAE dont like to play nice and should not be enabled together."

This is incorrect. Our Exchange 2003 servers use the following and are quite happy.

/PAE /3GB /USERVA=3030* /BASEVIDEO

*2970 in some cases after some PTE tuning

Without /PAE we never see over 3.75GB of physical memory installed on this hardware set, so it helps out a lot."

So I think Brad is going back to a issue back from Windows 2000 Server. Their use to be a issue when you addeded /3GB & /PAE together on DataCenter edition with more then 16 GB's of ram, it would cap you down to 16GB, regardless if you had More then that for memory..

Another issue with having both enabled is that /PAE increases the size of your PTE Size from 4 bytes to 8 Bytes...So when you have /3GB & /PAE together, in certain situations you can hurt yourself...

For Example..../3GB cuts down your nonpaged and pool paged memory and PAE will double your PTE Size. So if you do a Large File copy using the "Copy" command...You can incur a performance problem because you will be consuming Pool Memory at a faster rate because your PTE size is increased while your pool memory has decreased in size which might result in failed copies and depelted pool memory.

But on another note, in Windows 2003 SP1 (and servers with Hot-Add Memory), Windows will load the ntrknlpa (thats PAE kernel) by default. So essentialy you have PAE running on any newly built 2K3 Server with SP1+

re: Memory Management - Demystifying /3GB

Nudge — Thu, 12 Apr 2007 01:07:12 GMT

In a Windows 2003 server with sp1 and 16GB of RAM, I still need to use /PAE to allow the OS to address more than 3.75GB of RAM.

In this case is there any benefit to using /3GB? As there is more than enough RAM anyway, is there any point to limiting the Kernel to 1GB of RAM?

I would anticipate performance problems in this case.

What are everyone's thoughts?

re: Memory Management - Demystifying /3GB

Billy Dhillon — Thu, 12 Apr 2007 17:49:53 GMT

"In a Windows 2003 server with sp1 and 16GB of RAM, I still need to use /PAE to allow the OS to address more than 3.75GB of RAM.

In this case is there any benefit to using /3GB? As there is more than enough RAM anyway, is there any point to limiting the Kernel to 1GB of RAM?

I would anticipate performance problems in this case.

What are everyone's thoughts?"

I've seen that Issue on DEP enabled Proc's where you need to add the /PAE switch even if SP1 is installed (is this a HP Server by chance?).

As for adding the /3GB, what is the role of this server? You have to remember that /3GB is virtual Memory which is different the Physical memory. The Memory managment model works only in a 2GB/2GB (or 3GB/1GB) form. If their is nothing on your server that would take advantage of /3GB (any app that utilizes /largeaddressaware), then it would not benfit at all, it would likely degrade the performance of your box.

re: Memory Management - Demystifying /3GB

xentelworker — Thu, 12 Apr 2007 18:43:38 GMT

"In a Windows 2003 server with sp1 and 16GB of RAM, I still need to use /PAE to allow the OS to address more than 3.75GB of RAM.

In this case is there any benefit to using /3GB? As there is more than enough RAM anyway, is there any point to limiting the Kernel to 1GB of RAM?

I would anticipate performance problems in this case.

What are everyone's thoughts?"

If you don't have a DEP enabled processor, you will still need to add /PAE even if your have upgraded to SP1+

(Ref: http://support.microsoft.com/default.aspx?scid=kb;en-us;875352)

As for adding the /3GB, what is the role of this server?

You have to remember that /3GB is virtual Memory which is different the Physical memory. The Memory managment model works only in a 2GB/2GB (or 3GB/1GB) form.

If their is nothing on your server that would take advantage of /3GB (any app that utilizes /largeaddressaware), then it would not benfit at all, it would likely degrade the performance of your box.

What's going on with my Pagefile?

Ask the Performance Team — Tue, 15 May 2007 13:02:10 GMT

This is a follow-up to our Processes consuming high amounts of virtual memory post from January. Pagefile

re: Memory Management - Demystifying /3GB

Sashank — Mon, 21 May 2007 23:59:42 GMT

Is there some way to (programatically) find out when the OS is booted in the /3GB mode? The 32-bit version of my application sets a hard limit of 1700 MB after which it does not try to allocate any more memory. I'd like to switch this to 2700 MB when the /3GB switch is available. The best I can come up with till now is to read the boot.ini file, but I am wondering if there is anything clever out there, that I can do.

Thank you for the elaborate discussions on Windows Memory.

Sashank.

re: Memory Management - Demystifying /3GB

Digvijay — Thu, 21 Jun 2007 18:04:56 GMT

Nice Post..

helped me to clear a lot of doubt about the /3GB switch

Keep up the good work, Tim

re: Memory Management - Demystifying /3GB

xelox — Thu, 30 Aug 2007 03:21:56 GMT

Sashank: You can use powershell/wmi to get the value from boot.ini.

What About Terminal Server?

Gonzalo — Sun, 23 Sep 2007 04:31:32 GMT

Hi.

I Have a Windows 2003 SP2 Terminal Server with 2 GB in RAM and i haven't found a good advice in order to use (or not) the /3GB /Userva:3030 in a Terminal Server.

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re: Memory Management - Demystifying /3GB

Tim Newton — Fri, 05 Oct 2007 19:37:33 GMT

In response to Gonzalo's question, the answer is NO. You do not want to enable /3GB or USERVA unless you have a specific application need to do so, such as in an Exchange environment. On a terminal server, the last thing you want to do is cripple the kernel by enabling /3GB.

Gonzalo posted:

"I Have a Windows 2003 SP2 Terminal Server with 2 GB in RAM and i haven't found a good advice in order to use (or not) the /3GB /Userva:3030 in a Terminal Server."

re: Memory Management - Demystifying /3GB

Richard — Tue, 09 Oct 2007 17:10:16 GMT

Hi,

My servers have 17 GB of RAM and the /3GB /PAE switches enabled (vendors recommendation).

The BIOS shows 17 GB, but the OS only displays 15 GB. I thought the /3GB would limit to 16, but why 15 GB? Any ideas?

re: Memory Management - Demystifying /3GB

John — Wed, 24 Oct 2007 00:43:38 GMT

You wrote about Microsoft Exchange servers. Using Catia, a high end auto / aero CAD package, the recomendation has been to run 3 GB by default. Is this a problem? We commonly work with data files in the hundreds of MBs

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re: Memory Management - Demystifying /3GB

Louis — Wed, 16 Jan 2008 02:09:14 GMT

Is the /3GB Switch required in the 32-Bit Version of Windows 2003 R2????

re: Memory Management - Demystifying /3GB

wizualizacje architektoniczne — Mon, 04 Feb 2008 17:27:40 GMT

Thanks for that info.

Regards

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re: Memory Management - Demystifying /3GB

MarkR — Fri, 22 Feb 2008 22:15:28 GMT

After running the EXBPA, it recomends adding the /3GB to the Win2003 domain contollers in addition to the Exchange 2003 mailbox servers. What are the benifits to adding the /3GB to the DCs?

re: Memory Management - Demystifying /3GB

Cmonurz — Sat, 10 May 2008 13:37:52 GMT

Hi guy's, we get asked this a lot in the Terminal Services/Citrix world, where misguides admins add /3GB switch and cripple their servers.

Can you guy's confirm that in a 32bit Windows 2003 terminal services environment that this is a totally inappropriate modification?

Thanks!

re: Memory Management - Demystifying /3GB

Krishna — Thu, 15 May 2008 06:57:53 GMT

If my server has 32GB of RAM, is it possible to make IIS use all 32GB of RAM ?

re: Memory Management - Demystifying /3GB

Werner — Fri, 30 May 2008 22:08:31 GMT

So what is the maxinum amount of RAM that will work on a Intel Core2Duo with Win XP SP2 without any going to waste?

re: Memory Management - Demystifying /3GB

Manvendra Kumar — Mon, 30 Jun 2008 11:19:54 GMT

I have 4GB of ram installed and 3gb switch enabled. I am running SQL 2000. Few days back my server crashed. Is there any possibilities that it could have been caused due to 3gb switch limit settings. I couldn't find any errors through logs, event and dump analysis. If yes, what kind of error will indicate that it was caused due 3gb switch settings.

re: Memory Management - Demystifying /3GB

Anil — Sun, 13 Jul 2008 14:07:59 GMT

When configuring a new Exchange 2003 SP2 server on a Windows 2003 server with 4GB of RAM, what are the three settings that need to be changed in Windows to optimize memory?

re: Memory Management - Demystifying /3GB

Paulo Oliveira — Thu, 28 Aug 2008 17:05:15 GMT

So, this means that I don´t need the /3GB switch to make windows reconize up to 4GB? The OS will reconize automaticly?

Regards,

Paulo Oliveira.

re: Memory Management - Demystifying /3GB

timothyn — Wed, 03 Sep 2008 00:34:01 GMT

Paulo,

Yes, that is correct. The /3GB switch has absolutely nothing to do with how much physical RAM you have installed in the machine, simply how much VIRTUAL memory is allocated to user mode. The confusion over this is why I wrote this post in the first place.

re: Memory Management - Demystifying /3GB

jay f. — Thu, 18 Dec 2008 04:05:33 GMT

This was extremely helpful.

thanks

re: Memory Management - Demystifying /3GB

mmike — Thu, 29 Jan 2009 10:19:36 GMT

I added the switch to my XP Pro - I have 5GB ram installed - went to play Steam DOD online, program crashed with OS page pool report error followd by the Blue screen of Death

Good Posting - What can't Microsoft correct the Virtual memory and Physical memory issue -? Improvement with Windows 7???

re: Memory Management - Demystifying /3GB

Al S — Fri, 20 Feb 2009 09:55:00 GMT

Quick question on an old topic (and a darn excellent post I might add).

If I have a 32bit app running on a 64bit system is it still possible to get an OOM error? What I'm trying to find out.... is the 32bit app limited to 2GB even if it's running on a 64bit OS? Or will it not have a limit?

re: Memory Management - Demystifying /3GB

Senthil — Fri, 24 Apr 2009 14:22:43 GMT

If I install 20 or 25 GB of memory in windows 2003 servers,

What are the things I should need to change?and what is the size of the page file required?

Normally page file size is 1.5 times of RAM.(is it i require 37 GB of virtual memory for 25 GB RAM?)

re: Memory Management - Demystifying /3GB

Craig — Fri, 18 Sep 2009 17:51:35 GMT

You mentioned that you should use the /3GB switch when Exchange is installed on the server. What if Exchange is installed on a DC, should you still use it then? As I am sure I have read an article not to use the /3GB switch on a DC.

re: Memory Management - Demystifying /3GB

Aaron — Tue, 03 Nov 2009 12:53:39 GMT

This is simply the best blog i have read. I read this every few months to help refreshing myself and helping my 3GB Confused colleagues